Centrifugal supersonic compressor

ABSTRACT

A centrifugal supersonic compressor construction enables a high pressure ratio between the output and the input to be obtained. This compressor comprises an axial input stator, a rotor provided with a rotating diffuser, and a fixed diffuser which is a volute extended by a nozzle rectilinear in section. The rotating diffuser of the rotor consists of two coaxial discs connected together by radial blades, the radial dimensions of the blades and of the discs being such that the speed at the output of the diffuser rotating alone is slightly supersonic thereby obtaining a shock wave at the inlet of the nozzle.

United States Patent [191 Fabri et al.

[ CENTRIFUGAL SUPERSONIC COMPRESSOR [75] Inventors: Jean Fabri, Ville DAvray; Jean Friberg, Bourg-la-Reine; Raymond Siestrunck, Paris, all of France [73] Assignee: Compagnie Industrielle Des Telecommunications Cit-Alcated, Paris, France [22] Filed: Apr. 12, 1972 [21] Appl. No.: 243,371

[30] Foreign Application Priority Data Apr. 13,1971 France 71.12891 [52] U.S. C1 4l5/l09,415/143,415/181, 415/206, 415/219 A, 417/78 [51] Int. Cl. F04d 17/00, F04d 21/00, F04d 29/42 [58] Field of Search 415/109, 143, DIG. 1, 204, 415/206, 219 C, 219 A, 213, 74, 181, 88, 219 B [56] References Cited UNITED STATES PATENTS 704,756 7/1902 Ray 415/213 R 1,237,007 8/1917 Wilstam 415/109 1,670,065 5/1928 Eisenwinter 415/219 A 2,390,504 12/1945 Berger 1 415/213 R 2,786,261 3/1957 Schalyo, Jr. 415/206 2,845,216 7/1958 Sallou 415/213 R 2,962,206 11/1960 Borden et al. 415/D1G. 1 3,099,221 7/1963 Thompson 415/219 A [451 July 16, 1974 3,460,748 8/1969 Erwin 415/181 3,647,314 3/1972 Laessig 415/219 C 3,658,437 4/1972 Soo 415/219 A 3,692,426 9/1972 Ryall et a1. 415/219 B 3,759,627 9/1973 Ehlinger 415/219 A FOREIGN PATENTS OR APPLICATIONS 809,758 8/1951 Germany 415/109 733,533 7/1955 Great Britain 415/219 A 1,055,017 10/1953 France 415/143 1,188,110 3/1959 France 1 ..415/219A 1,294,817 4/1962 France 415/219 A 1,313,594 11/1962 France 415/DlG, 1 1,428,169 1/1970 Germany 1. 415/206 169,663 12/1959 Sweden 415/88 Zinn & Macpeak [5 7] ABSTRACT A centrifugal supersonic compressor construction enables a high pressure ratio between the output and the input to be obtained. This compressor comprises an axial input stator, a rotor provided with a rotating diffuser, and a fixed diffuser which is a volute extended by a nozzle rectilinear in section. The rotating diffuser of the rotor consists of two coaxial discs connected together by radial blades, the radial dimensions of the blades and of the discs being such that the speed at the output of the diffuser rotating alone is slightly supersonic thereby obtaining a shock wave at the inlet of the nozzle.

3 Claims, 5 Drawing Figures PATENT JULIEIQM ED mm 1 O 3 3,824,029

PATENTED L 1 61974 Y $824029 SHEH 3 UP 3 FIGS 1 CENTRIFUGAL SUPERSONIC COMPRESSOR RELATED APPLICATIONS A claim of priority under 35 U.S.C. 119 is made based on French application filed Apr. 13, 1971 No. EN 71 12 891 (Seine).

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a centrifugal supersonic compressor, particularly to one enabling a high pressure ratio between the outlet and the inlet of the machine to be obtained.

2. Prior Art It is known that in compressors of this type, the peripheral speed of the turbine blades, in relation to the cowling of the machine, becomes supersonic. In usual compressors of this type, the gas stream leaves the turbine at a high speed, and it is difficult to obtain satisfactory efficiency from the recompression shock wave.

In compressors of conventional design, regulation is difficult, because this regulation depends on several parameters.

SUMMARY OF THE INVENTION This invention provides a centrifugal supersonic compressor in which the friction of the gases against the wall of the stator is slight in relation to that of conventional centrifugal compressors so as to obtain improved efficiency.

The compressor according to the invention is, moreover, preferably intended for use in groups. It is desirable that the failure of a compressor in a group should not cause the stoppage of the other compressors of that group. Therefore, another aim of the invention is to produce a centrifugal supersonic compressor which can operate at a variable flow speed.

Another aim of the invention is to produce a compressor of the above defined type whose flow speed depends on a single parameter, which is consequently easy to determine.

Another aim of the invention is to produce a centrifugal supersonic compressor enabling a mach number having a high drive to be obtained, which can be used not only for the compression of heavy gases in which the speed of sound is relatively low, but also for the compression of air and other gases having relatively low density, being simply constructed and strong and having reliable operation and being free from surging.

For that purpose, the compressor in question, comprises in combination, a rotor provided with a rotating diffuser, a stator having an axial inlet provided with a fixed diffuser mounted as an extension to the rotating diffuser in the direction of a gas flow which is to be compressed, the fixed diffuser consisting of a volute extended by a nozzle tangentially connected to the said volute, the said rotating diffuser consisting of two coaxial discs connected by radial blades, the radius of the discs being greater than that of the blades, characterized in that the mutual radial dimensions of the blades and of the discs are such that the speed at the outlet of the rotating diffuser is slightly supersonic, the nozzle which has a sonic inlet section being a rectilinear diverging nozzle causing a recompression shock wave in the flow of the fluid in the vicinity of the connection nose of the noule and of the volute.

The use, in a rotating compressor, of a fixed rectilinear diffuser is known, but in that known technique, diffusers of that type are partitioned, generally by a great number of blades; on the contrary, in the compressor according to the invention, the fixed diffuser, both in its portion in the shape of a volute as in its rectilinear portion, has a smooth wall.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a centrifugal compressor according to the invention along line Il of FIG. 2;

FIG. 2 is a horizontal sectional view along line II-II in FIG. 1;

FIG. 3 is a sectional view taken along line IIIIII of FIG. 4 and showing a modification;

FIG. 4 is a cross-sectional view along line IV-IV of FIG. 3 of the modification;

FIG. 5 is a diagram showing the speed of the variation of the flow as a function of the compression ratio for an example of an embodiment of the compressor according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the embodiment shown in FIG. 1, the compressor comprises a stator 1 having an axial inlet 2. In this stator, is a rotor 3 mounted on a shaft 4, bearing, on the one hand, a front turbine 5 fitted with blades 5a and a drum 6 comprising two discs 7 and 8 connected together by a series of radial blades 9 defining, between them, rotating radial channels 9a. These blades have a smaller radial length than those of the discs, so that an annular diffuser space 10 is arranged at the periphery of that rotor. This rotating diffuser leads into a chamber having a spiral or volute shape 11 formed inside the stator, whose lateral walls are, either parallel or, as shown, slightly divergent.

This volute l1 constitutes a first portion of a fixed diffuser, which is connected to a second portion 12 of that fixed diffuser; this second portion consists of a rectilinear diverging nozzle whose inlet cross-section S, situated approximately at the connection nose between the volute' and the rectilinear nozzle, has a crosssection which is at least sonic, at the rated output of the machine. The compression at that point, is provided by a shock wave generated at the volute nose.

Preferably, the rotor comprises, moreover, auxiliary blades such as 13 and 14, fixed respectively to the outside walls of the disc 7 and 8 and recessed partly in cavities l5 and 16 having an appropriate shape arranged in the inside wall of the stator.

This embodiment of the compressor operates as follows.

The fluid to be compressed enters through the axial inlet 2, and is driven by the front turbine 5 and enters the rotating channels 9a where it is subjected to centrifugal force which drives it out towards the rotating annular diffuser 10. This fluid, on leaving the channels 9a begins to slow down-with slight losses, the movement of the gas, in relation to the mobile walls which limit it, being appreciably subsonic. In this rotating diffuser, the wakes behind the blades and the undisturbed gas currents coming from the mobile channels mix together and the kinetic energy imparted to the fluid by the blades 9 of the rotor begins to be transformed into pressure energy; the losses caused by that transformation,

which are due to the viscosity of the fluid, are relatively slight.

Nevertheless, it would not be possible to effect all the diffusion in this manner, for it would be necessary to use a rotating diffuser having a very great relative radius, and the result would be a great increase in the friction losses, this entailing the risk of losing the benefit of the solution adopted.

The fixed diffuser 11, 12, which is not partitioned, fulfills the essential function of channeling the fluid leaving the rotating diffuser, this fluid still moving at high speed, and of recuperating that kinetic energy as much as possible. The continuously varied shape of the lateral walls chosen for this diffuser enables energy losses to be avoided as much as possible.

The regulating of the flow can be determined'easily by the accurate choice of a single passage section S, whereas in partitioned diffuser compressors, the flow is limited by the sum of the minimum sections between the blades. The single channel solution is particularly easy to implement, and experience shows that the absence of blades prevents the non-adherence of the fluid which constitutes a cause of instability at low output. Therefore a supersonic compressor of a new type, simple, having a high efficiency, and whose output can be predetermined accurately is thus obtained by combining a rotating diffuser and a fixed diffuser comprising a volute and a diverging nozzle. Experience shows that this machine is, moreover, free from surging.

The additional blades l3and l4 prevent leakages and enable a high compression ratio to be maintained. By way of an example, a freon 114 compressor (in which the sound propagation speed is, at 50 C, l30/Sec.) made according to the invention, enables a pressure ratio of 8 with a peripheral speed equal to 230 m/sec. at the blade tips to be provided between the outlet and the inlet.

These advantages are obtained mainly due to the fact that a slowing down, hence, a compression, occurs in the rotating diffuser, the speed now being only slightly supersonic at the outlet of that rotating diffuser, the ratio passing, for example from 3 to 5 in the rotating diffuser to pass subsequently from 5 to 8 in the fixed diffuser assembly, the shock wave(s) being formed substantially at the section S, and the nozzle 12 being formed quite long so that the compression may determine ratios up to 8 provided in this example of an embodiment.

The efficiencyof the machine is improved due to the fact that, in the rotating diffuser, the tangential flow speed of the fluid is reduced to a level which is only slightly greater than mach l, the efficiency for that transformation being high, for example, in the order of 0.9.

The friction on the walls of the stator is lower than that which is found in conventional designs. The use of the rotor diffuser makes it possible to avoid surging, and consequently enables a variable output and more particularly enables the operation of the compressor when one of the compressors of the group of compressors to which the compressor in question belongs ,breaks down.

FIG. 5 is an example of a curve obtained by means of a compressor according to the invention in a constant speed test; the flow speeds are marked in the abscissa, and the compression ratios P are marked in the ordinates. The continuous portion of the line represents the normal operation zone of the compressor, in which the flow (DN) is practically independent from the compression ratio; this flow can therefore be considered as constant, and constitutes a characteristic of the machine.

As the speed is still high at the nose of the nozzle at S, it is possible to make the device in the form of a modification shown in FIGS. 3 and 4 comprising an ejector 21 in which the flowing gas, driven out by the volute at S, is used as a primary flow driving a recycling flow to be re-injected.

In that modification, the device comprises a reinjection nozzle 22 which leads into the nose S of the rectilinear nozzle 12, the flow to be re-injected being brought to f, and being driven by the primary flow F leaving the volute and entering the nozzle.

A gas, or possibly two different gases can be sucked in through two inlets at different pressures, there being a single output. Different pressure ratios can therefore be obtained for the two gases f and F, for example 8 for the main flow F, 1.2 for secondary flow f.

Apart from the difference in construction which results therefrom for the fixed part, enabling the injector to be added, the other characteristics of the machine manufactured according to this modification are identical to those of the first embodiment.

The invention is not limited to the embodiments illustrated and described, which have been chosen only by way of examples.

We claim:

1. A centrifugal compressor which is supersonic at rated output, said compressor comprising in combination:

a stator,

a rotor mounted for rotation about its axis within said stator,

said rotor being in the form of a drum and including spaced opposed discs whose similarly curved inner surfaces relative to each other define therebetween a gas flow path which changes from axial'to radial,

a plurality of circumferentially spaced blades carried by said rotor and extending between said rotor discs from the vicinity of the compressor axis throughout that portion of the flow path which changes from axial to radial,

said discs having their periphery extending radially outward beyond the outboard edges of said blades to form disc extensions defining a rotary diffuser,

and wherein the mutual radial dimensions of the blades of the discs are such that the speed of the compressed gas at the outlet of the rotating diffuser is slightly supersonic at rated output,

said stator including a fixed diffuser positioned as an extension to the rotary diffuser in a direction of a gas flow which is to be compressed,

said fixed diffuser comprising a vaneless volute circumferentially surrounding said rotor and a rectilinear diverging nozzle connected tangentially to said volute, said vaneless volute having a peripheral spiral wall of continuously increasing diameter leading to said nozzle, and said nozzle having a sonic inlet means at the end of said volute at rated compressor output,

said auxiliary blades being received within said annular recesses to create dynamic seals therebetween and eliminate backflow of the pressurized fluid to the compressor inlet.

3. Compressor according to claim 1 in which the rotor includes a front turbine with a set of blades mounted on the upstream side of the rotating drum rotor and attached to the rotor. 

1. A centrifugal compressor which is supersonic at rated output, said compressor comprising in combination: a stator, a rotor mounted for rotation about its axis within said stator, said rotor being in the form of a drum and including spaced opposed discs whose similarly curved inner surfaces relative to each other define therebetween a gas flow path which changes from axial to radial, a plurality of circumferentially spaced blades carried by said rotor and extending between said rotor discs from the vicinity of the compressor axis throughout that portion of the flow path which changes from axial to radial, said discs having their periphery extending radially outward beyond the outboard edges of said blades to form disc extensions defining a rotary diffuser, and wherein the mutual radial dimensions of the blades of the discs are such that the speed of the compressed gas at the outlet of the rotating diffuser is slightly supersonic at rated output, said stator including a fixed diffuser positioned as an extension to the rotary diffuser in a direction of a gas flow which is to be compressed, said fixed diffuser comprising a vaneless volute circumferentially surrounding said rotor and a rectilinear diverging nozzle connected tangentially to said volute, said vaneless volute having a peripheral spiral wall of continuously increasing diameter leading to said nozzle, and said nozzle having a sonic inlet means at the end of said volute at rated compressor output, whereby; a recompression shock wave is caused in the flow of the gas in the vicinity of the connection of the nozzle to the volute.
 2. The compressor according to claim 1, wherein said stator includes wall portions conforming to the outer surfaces of the discs and being slightly spaced therefrom, said wall portions including annular recesses within the same opposite said discs, and discs including auxiliary blades fixed to the outer surfaces thereof with said auxiliary blades being received within said annular recesses to create dynamic seals therebetween and eliminate backflow of the pressurized fluid to the compressor inlet.
 3. Compressor according to claim 1 in which the rotor includes a front turbine with a set of blades mounted on the upstream side of the rotating drum rotor and attached to the rotor. 